You should be able to go into the control panel and go to Mice and pointing devices and change the sensitivity of your touchpad. My suspicion is that it is currently too sensitive and as a result, when you rest your palms on the lower shell while typing, there is enough pressure on your touchpad to cause the mysterious moving cursor.
Also, check out this site for more information and troubleshooting tips that should be able to help you:
I hope this helps!
Windows Outreach Team